The present invention relates to an improved waste gas treatment system and process.
Conventional biological technology for treating waste gas, such as a biofilter and a biotrickling filter, can only deal with the waste gas having little or no dust/grease. When the waste gas to be treated contains dust/grease, it will clog the biofilter, reduce the activity of the microorganisms (or activated sludge), cause the short flow of the reactor, increase the pressure loss, decrease the treating efficiency and shorten the service life of the bioreactor. Therefore, the conventional biological technology for treating waste gas is often limited to the application of treating waste gas in a specific field.
Nowadays the types for waste gas entering a bioreactor include “flow upward (i.e., flowing upward from the bottom of the reactor)” and “flow downward (i.e., flowing downward from the top of the reactor).” The type of “flow upward” can better control the pH value to avoid the phenomenon of acidification, and therefore maintain the higher activity of the microorganisms in the whole biofilter. However, for the type of “flow upward,” it is not easy to control the humidity of the filter materials, which often causes the deficiency of the humidity for the filter materials at the inlet of the reactor. In addition, because the type of “flow upward” takes an opposite direction with respect to the normal water flow, the distribution of the gas flowing into the reactor is even worse, which will result in the phenomenon of short flow (i.e., the gas fails to flow through the whole cross section of the biofilter, but only flows through the passages having least resistance), and decrease the whole removal efficiency of the system. To the contrary, the type of “flow downward” can better control the humidity of the filter materials and perform a better distribution of the gas flow. However, because the type of “flow downward” takes a same flowing direction as the gravity, the filter materials can be denser, which increases the resistance for the gas flowing therethrough and therefore forms a greater pressure loss, and increases the operational cost and the maintenance cost of the inlet fan.
In addition, the numbers of the emission of the bioaerosol from the biofilter depends on the effects of the immobilization of the filter materials as employed (filled). For example, the numbers of the emission of the bioaerosol from a common peat biofilter can be up to 107 CFU/m3− air, whereas that from an activated carbon biofilter can be 105 CFU/m3− air, which is a little lower than the peat biofilter. If the microorganisms in the reactor are not microorganisms commonly seen indoors or outdoors, it may be harmful to the environment and even to the humanÿ s life when its numbers exceeds a certain extent.